Tufted carpets generally comprise a backing, face yarn and a binder. The face yarn penetrates the backing such that a plurality of tufts projects from one side of the backing and a plurality of face yarn stitches is disposed on an opposite side of the backing. The binder is present on the stitched side, anchoring tufts in and to the backing. Many carpets also include an additional backing for added stability. In those carpets, face yarn typically penetrates a primary backing, as described above, and an additional backing, such as a relatively open weave secondary backing fabric, is secured to the stitched side with the binder. Alternative structures in which face yarn penetrates a composite backing made up of two or more individual components, such as superposed dual primary backings or primary and secondary backings, also are well known; a recent example is disclosed in International Application WO 98/49000. In manufacture of carpets, a backing is tufted with face yarn and the stitched side of the tufted backing is typically coated with a liquid binder formulation capable of being cured to form a solid binder that anchors tufts to the stitched surface or between that surface and an additional backing. The binder, both before and after curing, is commonly referred to as a “backcoat.”
Currently, woven polypropylene fabrics are most commonly used as backings. Face yarns comprise a plurality of filaments and are typically continuous multifilament yarns or spun yarns formed by spinning staple fiber into yarn. Filaments of yarns most commonly used as face yarn comprise synthetic resins, such as nylon, olefin, polyester and acrylics, although natural fiber yarns such as wool yarns are also used. Conventional backcoats used in carpet manufacture are most commonly particulate-filled, aqueous latexes of organic polymer compositions that set up or cure on heating to drive off their aqueous contents. Crosslinkable styrene-butadiene copolymers are most commonly used as the organic polymer of the backcoat formulations. The particulate filler most commonly is calcium carbonate and typically is present in the latexes in significant amounts (e.g., 60–85 weight %) to impart viscosities high enough to allow application of backcoats uniformly over the entire surfaces of intermediate carpet structures with simple equipment during carpet manufacture.
Although carboxylated styrene-butadiene copolymers are most commonly used in filled latex binders due to cost and performance, the cured binders are deficient due to their uptake of water and tendency to lose considerable strength when wet. In finished carpets with such binders, contact with water, for example from spills and splashes, can lead to marked losses of tuft lock or tuft bind such that face yarn tufts are easily pulled out of the carpets. It has been proposed to reduce or eliminate the use of filled, aqueous latex binders by use of binders based on thermoplastic resins. In general, proposals of this type involve bonding the face yarn stitches to a backing or backings by cooling a softened or melted thermoplastic resin in contact with the stitched side of a tufted backing and, when used, with an additional backing, to solidify the resin. Thermoplastic resins used for adhering the stitches and the backing are those that exist in solid form at temperatures normally encountered during use of carpets but can be softened or melted in contact with backings and face yarn stitches, or softened or melted and then contacted while softened or melted with the backings and stitches, at temperatures low enough that the other components of the carpets are not damaged. Thermoplastic binders comprising such resins can be provided in solid form, such as a film or coating on or applied to backings, as powder or loose fiber applied to the backings or stitches, as loose fiber needled or otherwise affixed to backings, and as fabrics secured or applied to the backings or their stitched sides. The binders can also be provided with the resin thereof softened or melted, for example by extruding melted resin formulations directly onto the stitched side of a backing or by laminating a tufted primary backing to a secondary backing with softened or melted resin formulations applied to or between the backings as they are brought together. Carpets made using such binders are more resistant to loss of strength due to water uptake than carpets with conventional, cured carboxylated styrene-butadiene copolymer binders. Such alternative binders also can offer advantages over conventional carpets because thermoplastic binders are better suited for recycle to melt processing operations than conventional binders. Thus, while face yarns and backings most commonly used in carpets are composed primarily of thermoplastic resins capable of being reused in melt-forming operations, cured latex binders typically contain levels of crosslinked polymer solids that can make such reprocessing impractical due to burning, smoking and impairment of flow of melted resins.
AdBac® Composite System carpets with backings made and sold by Amoco Fabrics and Fibers Company are an example of known carpets with thermoplastic binders. In one embodiment, AdBac® System carpets use a light weight nonwoven web of filaments of a thermoplastic resin needled to a woven polypropylene carpet backing. After tufting the needled backing with face yarn, the structure is heated to melt the resin of the filaments of the web such that the melted resin flows around the face yarn stitches and their junctions with the backing. The resulting structure is cooled to solidify the melted resin, thereby anchoring the tufts and, when a secondary backing is also used, securing it to the stitched side of the tufted backing. Alternative AdBac® Composite System carpets have stitches and backings adhered through use of woven secondary backing fabrics coated with lower melting thermoplastic resin compositions that can be melted and cooled in contact with the stitched side of a tufted primary backing to secure the tufts and laminate the backings. AdBac® System carpets have better tuft lock retention when wet than conventional carpets. They also are lighter, more flexible and easier to handle than conventional carpets with their mineral-filled, cured latex binders and, therefore, easier to install. They also can be installed over a considerably broader range of temperatures and their backings and binders afford greater potential for melt reprocessing in carpet manufacture. Commonly assigned International Application PCT/US96/03485 discloses carpets, backings and carpet manufacture involving binders comprising thermoplastic resins and substantially free of latex and mineral fillers, including AdBac® Composite System carpets and backings and binders therefor.
Other proposals and concepts for carpets prepared using softened or melted thermoplastic resin compositions that are cooled in contact with face yarn stitches of a tufted backing and/or a secondary backing to help secure tufts and/or bond primary and secondary backings are found in commonly assigned U.S. Pat. No. 4,844,765, disclosing lamination of tufted primary carpet backings to secondary backings with a composite hot melt adhesive sheet made up of adhesive formulations with higher and lower melt viscosities; U.S. Pat. No. 5,240,530, disclosing lamination of tufted primary backings to secondary backings with a sheet of extruded isotactic polypropylene; U.S. Pat. No. 5,532,035 disclosing tufted fabrics of a single type of thermoplastic material in which a primary backing of nonwoven polyester fibers and lower melting polyester binder fibers is tufted with polyester face yarn and the tufts are anchored and a secondary backing is laminated by partial melting of the primary backing and then cooling the same; and European Patent Application 80304253.0 disclosing tufted pile fabrics in which tufts are secured to a primary backing and an anchor coat is formed by needling or otherwise applying to both surfaces of the backing a layer of low melting nylon or other fibers, tufting the backing with the applied layer of fibers, and melting the layer on the side of the backing opposite the pile surface.
A difficulty with carpets with thermoplastic binders, however, is their tendency to fuzz during use. Fuzzing occurs when individual filaments of yarn tufts pull completely or partially out of the tufts and manifests itself in a fuzzy appearance and pilling of the carpet pile and, in time, an uneven, thinning appearance. For many types of carpets, fuzzing is encountered less frequently and severely in carpets prepared with conventional aqueous latex binders. The difference may be related, at least in part, to different properties and behaviors of the softened or melted resins of thermoplastic binders and of aqueous liquid latex formulations as used as binders in carpet manufacture.
In the case of conventional aqueous latex binders, their liquid nature makes uniform application easy and inexpensive. Flow properties are easily controlled to achieve effective coating of stitched backing surfaces and wetting of filaments of the stitches by simple adjustment of filler, polymer and water levels of the formulations. Unfilled or low viscosity latex formulations are sometimes used in conjunction with conventional highly filled formulations. In most carpet constructions and with most common materials of construction, heating to drive off water and cure the latex binders results in good bonding of stitches to backings and of filaments within stitches. Surfactants can also be used to adjust surface tensions of binder formulations in relation to tuft stitches and backings. It also is known from U.S. Pat. No. 4,654,247 to prime face yarn stitches for application of latex binders by applying in advance of the binder an aqueous dispersion of surfactant or polymer with surface tension less than or equal to that of the face yarns; the primer is reported to promote uptake of binder by face yarns and reduce fuzzing of yarns that resist penetration by binders due to treatments against soiling, staining, mold, mildew and static buildup.
With thermoplastic binders, in contrast, dispersibility, flow properties and affinity to backings and face yarns of melted thermoplastic resins are less conducive to effective application and bonding. In some cases, uniform application of thermoplastic binders is hindered by their physical form. For example, thermoplastic binders in the form of loose fiber are difficult to apply consistently and uniformly over stitched backing surfaces; melting and cooling of the resin of the fibers can produce irregular gaps and thick and thin areas of binder, leaving entire stitches or groups of stitches unbonded or only superficially bonded. Powdered thermoplastic binders can be applied somewhat more uniformly than loose fibers but special equipment is usually needed. Thermoplastic films, sheets, coatings and nonwoven fabrics tend to be more effective, not only because their sheetlike or fabric form makes them well suited for application to the entire stitched side of a tufted backing, but also because they can be prepared to provide the thermoplastic binder resin in consistent weights per unit area tailored to carpet and manufacturing requirements. However, even the more uniformly applied thermoplastic binders suffer due to high viscosities and poor flow of their melted resins as compared to the liquid latex binders. Surface tensions of the melted thermoplastic resins can also lessen affinities to face yarns and backings and are not as easily adjusted as those of conventional aqueous latexes. High flow rate resins, special resin compositions, application of pressure to intermediate carpet structures to promote flow and improve distribution of melted resin, special application techniques and other measures can provide improvement but not to the degree desired and usually not without equipment modifications, added process complexity and increased cost.
Whatever the cause or causes, fuzzing in carpets with thermoplastic binders remains a problem and an obstacle to more widespread realization of the benefits of such carpets. There is a need for improvement so that filaments of face yarn tufts are more effectively held in the carpets.